MORE ACCURATE CHRONOLOGICAL AGE-DETERMINATION OF CRUSTACEANS FROM FIELD SITUATIONS USING THE PHYSIOLOGICAL AGE MARKER, LIPOFUSCIN

A captive population of Australian red-claw crayfish, Cherax quadricarinatus, of known age was used for the study. Lipofuscin concentration in the left olfactory lobe cell mass of the brain was measured using image analysis of fluorescence micrographs. Age predictions based on lipofuscin concentration were more accurate and had narrower 95% confidence limits than those derived from the more conventional body size and weight predictors for all age groups tested (180, 300, 420, 780 d). Overall, use of lipofuscin concentration produced a significantly lower (p < 0.001) mean age-prediction error (16.65%)than use of carapace length or body weight (32.45 and 32.3%, respectively). Carapace length was of little value for prediction of the age of older individuals. Mathematical models defining the relationships between temperature, age and lipofuscin accumulation were derived from laboratory-reared individuals. These models did not describe adequately the course of lipofuscin accumulation in crayfish from the field over the whole lifespan. Field data from three ''known'' year-classes were used to generate simulated size-frequency and lipofuscin concentration-frequency histograms. Year-classes in the lipofuscin concentration frequency-histogram were much more easily distinguished than in the size-frequency histogram. Under field conditions, lipofuscin concentration was a better predictor of chronological age than conventional morphometric measures.